Closet flange in new construction

I'm planning to install a Toto Drake (purchased from Terry) in a new house. (I've replaced an existing toilet but never set one in new construction). The rough-in was done by a contractor. The closet flanges have what looks like an integral plug for hydraulic testing. The plug moves a little but I wasn't able to figure out how to remove it and didn't want to risk the brute force method. Or am I just supposed to knock out the center portion (which looks like thin ABS)?

Most of the flanges out there do have what they call a knock out. Just be careful not to lose it down the line. If you could post a pic of it we could be more sure if the one you have is a knock out type.